1. Field of the Invention
This invention relates to a reproducing apparatus having a recording speed discriminating system and, more particularly, to an apparatus arranged to reproduce signals recorded on a recording medium with a plurality of rotary heads.
2. Description of the Prior Art
Among the conventional video tape recorders (hereinafter will be called VTR's), there have been the kind selectively using two or more different tape moving speeds in recording or reproducing signals. Some of them, such as the VTR's called VHS type, are arranged to be capable of recording over different periods of two and six hours. In the VTR of this kind, the width of a magnetization track, i.e. track width, obtained according to the recording format of a six-hour mode is only 1/3 of the track width obtained by the format of a two-hour mode. Meanwhile, with the same head and tape system used, the S/N ratio of a reproduced picture is determined by a sliding noise, the noise of the apparatus, the track width, etc. Therefore, a wider track width is preferable in terms of the S/N ratio. Hence, reproduced picture quality obtainable by the six-hour mode is inferior to the quality obtainable by the two-hour mode. In view of this, some of the conventional VTR's are arranged to record or reproduce signals in the two-hour mode in cases where a high reproduced picture quality is required and in the six-hour mode when no particularly high quality is required.
Change-over between the two- and six-hour modes is effected by changing the tape moving speed as mentioned above. The tape speed is arranged to be manually changed in recording according to the recording purpose of the operator or to be automatically changed by utilizing a reproduced control signal. The control signal is a signal of 30 Hz which is obtained by frequency dividing a vertical synchronizing signal contained in a video signal and is longitudinally recorded along a recording tape. In recording a signal f of a given frequency on a tape, the recording wavelength [ on the tape depends on the tape speed Vt. This relation can be expressed as Vt=f. Accordingly, with the control signal of 30 Hz recorded, the frequency of the signal reproduced at the same tape speed as a speed employed in recording is also 30 Hz. In case that signal recorded at a tape speed of the two-hour mode is reproduced at a tape speed of the six-hour mode which is 1/3 of the recording tape speed, the frequency of the reproduced signal is 10 Hz. Conversely, when the signal recorded in the six-hour mode is reproduced in the two-hour mode, the frequency of the signal reproduced is 90 Hz. Therefore, the tape speed employed in recording can be found by measuring the period of the reproduced control signal. This is the principle of the tape speed discriminating method of using the control signal.
The principal purpose of the control signal is to control the rotary video head or a tape driving system in such a way as to have the head accurately trace the recording tracks during a reproducing operation. The tracking control method of using the control signal has been well known. However, the tracking control system using the control signal is incapable of giving information on the recording track position obtained at each specific moment although it gives averaged information on the track position.
VTR's have recently been trending toward recording with increased recording density. As a result of this trend, there has been proposed a method of performing tracking control without arranging any separate area for recording the control signal. The VTR adopting this method is, however, incapable of discriminating the tape speed by the above-stated conventional method in cases where a plurality of different tape speeds are selectable for recording and reproduction. Therefore, there have arisen the need for a new tape speed discriminating method for solving these problems.